Citations Report Website, the top 17 Journals by JIF in 2011 were chosen for the study. All manuscripts' ... categorized based on its research design (Retrospective, Review, etc). ..... JIF of journals linked to professional societies had a higher ...
Vol. 41 (6): 1058-1066, November . December, 2015 doi: 10.1590/S1677-5538.IBJU.2014.0497
Factors associated with the Journal Impact Factor (JIF) for Urology and Nephrology Journals _______________________________________________ Joseph M. Sewell 1, Oluwakayode O. Adejoro 1, Joseph R. Fleck 1, Julian A. Wolfson 2, Badrinath R. Konety 1 Department of Urology, University of Minnesota School of Medicine, Minneapolis, MN, USA; 2 School of Public Health, Division of Biostatistics, University of Minnesota School of Medicine, Minneapolis, MN, USA 1
ABSTRACT ARTICLE INFO ______________________________________________________________
Purpose: The Journal Impact Factor (JIF) is an index used to compare a journal’s quality among academic journals and it is commonly used as a proxy for journal quality. We sought to examine the JIF in order to elucidate the main predictors of the index while generating awareness among scientific community regarding need to modify the index calculation in the attempt to turn it more accurate. Materials and Methods: Under the Urology and Nephrology category in the Journal Citations Report Website, the top 17 Journals by JIF in 2011 were chosen for the study. All manuscripts’ abstracts published from 2009-2010 were reviewed; each article was categorized based on its research design (Retrospective, Review, etc). T and correlation tests were performed for categorical and continuous variables respectively. The JIF was the dependent variable. All variables were then included in a multivariate model. Results: 23,012 articles from seventeen journals were evaluated with a median of 1,048 (range=78-6,342) articles per journal. Journals with a society affiliation were associated with a higher JIF (p=0.05). Self-citations (rho=0.57, p=0.02), citations for citable articles (rho=0.73,p=0.001), citations to non-citable articles (rho=0.65,p=0.0046), and retrospective studies (rho=-0.51,p=0.03) showed a strong correlation. Slight modifications to include the non-citable articles in the denominator yield drastic changes in the JIF and the ranking of the journals. Conclusion: The JIF appears to be closely associated with the number of citable articles published. A change in the formula for calculating JIF to include all types of published articles in the denominator would result in a more accurate representation.
Key words: Journal Impact Factor; Urology; Nephrology; Periodicals as Topic
INTRODUCTION The Journal Impact Factor (JIF) is an index annually published by The Journal Citation Reports (JCR). It was established by Eugene Garfield to compare investigators’ and journals’ research influence on its time (1). The JIF for a particular journal is calculated by the ratio of total number
Int Braz J Urol. 2015; 41: 1058-66
_____________________ Submitted for publication: October 03, 2014 _____________________ Accepted after revision: March 26, 2015
of citations received in a determined year to the total number of citable articles published by that journal in the previous 2 years (Figure-1) (2, 3). The non-citable articles criteria include editorials, news, meeting reports, etc. Original research and review articles are the only article types that meet the definition of citable articles according to the Institute of Scientific Information (3, 4). Web of
ibju | Journal Impact Factor (JIF) of Urology and Nephrology Journals
Figure 1 - JIF Calculation formula.
Science (Thomson Reuters Inc.) is a citation service accessible through an indexing database and search engine, ISI Web of KnowledgeSM (WoK) (5-9). The numerator of the JIF formula includes the citations of all articles of a given journal whereas its denominator excludes the number of non-citable articles published; thus making the formula potentially manageable. While this flaw has been regarded as insignificant by the index creator, it has also generated significant debate and skepticism among editors and authors who disagree. The creator himself has accepted the issue yet considering it “statistically significant only in rare cases” (2, 10-14). The exclusion of non-citable articles from the denominator can hypothetically improve the JIF by increasing the number of self-citations, non-citable articles or reducing the number of citable articles (15-17). Regardless of this situation, the JIF is held as the gold standard measure to judge journals’ quality with a general lack of awareness of its formula, purpose, and meaning. All of which is now coming under greater scrutiny (18-21, 14). This debate is not merely academic as many universities are now using “publishing in high JIF journals” as an evaluation criterion for promotion. Publication in high JIF journals also affects success in competing for extramural grant funding (22). We sought to examine the JIF among nephrology and urology journals in order to elucidate the main predictors of the index while generating awareness among scientific community about the current formula used to calculate the JIF and its flaws. We also attempt to show that small discrepancies in the formula do influence the overall calculation and the subsequent ranking list. MATERIALS AND METHODS Journal Selection The top 40 journals ranked by JIF in the Journal Citation Reports for 2011 in the urology
and nephrology category were selected for the study. We excluded journals that were not published in English and published articles of one specific kind of research design (basic science, retrospective studies, review articles). Twenty-three journals out of the 40 journals initially selected were excluded for containing only review (16) and basic research (7) publications. Variables Selection All of the archived abstracts from each journal’s website for years 2009-2010 were individually reviewed. This is the period used for JIF calculation that is reported for 2011. We categorized each of the articles according to research design (basic science, non-clinical experimental and translational research, clinical trial, retrospective study, prospective study, case report and case series, cross-sectional study, review article, meta-analysis, systematic review, and guideline). If the study design could not be ascertained from the abstract, the manuscript’s methods section was read in order to obtain a more precise classification. Appendix 1 outlines the articles’ sorting criteria for research design (Appendix 1). The number of self-citations, citable and non-citable articles, and citations made to citable articles, and citations made to non-citable articles were also identified (15, 16). Other variables examined included society affiliation, US vs. non-US journals, number of articles published by the journal, average pages per issue, and US and non-US articles. ISI Web of KnowledgeSM Citations Data Validation Data values for JIF, self-citations, citable and non-citable articles published during 2009 and 2010, as well as the total number of citations used to calculate the 2011 JIF were retrieved and examined from the JCR web site (7, 8). The JCR website, however, did not individually disclose the citations made to citable and non-citable articles that were used to calculate the 2011 JIF. As an
ibju | Journal Impact Factor (JIF) of Urology and Nephrology Journals
alternative, two other databases (Web of Science and MEDLINE) from the WoK website were used (5, 6, 9). The data for US and non-US articles was also acquired through the WoK website (6, 9). Because the sum of citations to citable and non-citable articles (total number of citations) retrieved from the WoK website did not directly match the total number of citations acquired from the JCR website, we sought to validate the WOK website data by generating an alternative JIF utilizing the data extracted from the WOK website. The goal for this intermediate step was to accurately use the WOK website data a posteriori during our statistical analysis in lieu of the JCR website data (not individually disclosed). The alternative JIF was calculated using the citations data acquired from the WoK website. This JIF was correlated with the official JIF published by JCR through the Spearman’s rank-order correlation test. A correlation with a p-value less than 0.05 and a slope close to 1 were defined as the required criteria for validation. Statistical Analysis The number of articles published during 2009 and 2010 issues published per year, average pages per issue, self-citations, issues published per year, average articles published per issue, citations made to citable articles, citations made to non-citable articles, and the categorical variables were analyzed as independent variables. All other continuous variables were analyzed as a ratio relative to the total number of publications in the period of interest (i.e. ) because they depended on the total number of articles published. The association between the variables and JIF was examined using the JIF as the dependent variable. A two tailed Welch’s t-test and Spearman’s rank-order correlation test were performed for categorical and continuous variables respectively. All variables were then included in a multivariate linear regression model using a stepwise variable selection method. An alternative multivariate model excluding the counts for citable articles was analyzed in order to account for
co-linearity of other variables with the variable “citable articles”. A hypothetical JIF (JIF´) was created with the data obtained from the JCR website, one that includes the non-citable articles in the denominator of the index calculation (Citations made to Citable and Non-citable articles/Citable and Non-citable articles). A Welch’s t-test was also used to compare the JIF published by the JCR with the hypothetically created JIF. All computations were performed using SAS 9.3 (SAS Institute, Cary, NC). P-values of